In a conventional wireless communication system in which mobile stations send and receive data to and from base stations, when a mobile station sends data to a base station, the mobile station requests scheduling from the base station before the mobile station sends the data. For example, in data transmission using a physical uplink shared channel (PUSCH), first, a mobile station sends a scheduling request (SR) and then requests the base station to allocate the communication resources. The base station sends back a Grant that indicates authorization of the request and then notifies the mobile station of authorization of the allocation. The mobile station that has received the notification sends a buffer status report (BSR) to the base station, whereby the mobile station notifies the base station of the volume of the data to be sent. If the base station permits the data to be received, the base station sends back a Grant to the mobile station, whereby the base station notifies the mobile station that the data transmission is permitted. When the mobile station receives the Grant, the mobile station enters a state in which the station can use a PUSCH to perform the data transmission.
In the series of the processes described above, because there is a need to calculate the volume of data to be transmitted both when the BSR is transmitted and when the Grant with respect to the BSR is sent back, the processes take a relatively long time (for example, 8 ms). In particular, when the volume of data is small or when data transmission is resumed after a transmission is temporarily suspended, because the percentage of the BSR transmission time with respect to the communication time (approx. 40 ms) is high, this time period results in the occurrence of a transmission delay. There is a known technology for reducing this delay factor. In this known technology a base station retains therein, in an associated manner, the reception timing of an SR and a BSR and then specifies a BSR from the time at which the SR is received, whereby the process for sending and receiving the BSR is eliminated.    Patent Document 1: Japanese National Publication of International Patent Application No. 2010-518733
However, with the technology described above, because an SR with a specific timing is associated with a BSR, it is conceivable to perform signaling on a higher layer, such as layer 1. Furthermore, when the base station detects the BSR described above, in addition to a usual (initial) SR, the base station receives, from the mobile station, another SR that is used to specify the BSR. Consequently, the transmission time period of the SR that is sent from the mobile station becomes long and thus the delay time may sometimes increase. For example, when the transmission time period of an SR is 20 ms and the amount of resources for the SRs is that corresponding to 200 mobile stations, if all of the mobile stations send, in addition to the usual SRs, another SR that is needed to specify a BSR, the amount of the resources consumed for the SRs increases by a factor of two. Consequently, the amount of the resources for the SRs corresponding to 200 mobile stations is decreased to an amount corresponding to 100 mobile stations. Thus, in order to reserve, as before, the resources for the SRs by an amount corresponding to 200 mobile stations, the wireless communication system changes the transmission time period of the SR from 20 ms to 40 ms. Consequently, the transmission delay time for each mobile station increases by 20 ms (=40-20 ms).